The present invention relates to a so-called moisture-responsive resistor element in which the electric resistance is changed depending on the humidity. More particularly, the present invention relates to a moisture-responsive resistor element of the direct current driving type for measuring the relative humidity.
A moisture-responsive resistor element is utilized for not only a hygrometer but also an apparatus in which electric control is automatically performed according to the change of the humidity, for example, a drier or dehumidifier.
As a conventional moisture-responsive resistor element, there is known an element formed by mixing a metal oxide with a catalyst or mixing metal oxides together, fixing the mixture to a substrate or coating a paste of the mixture on a substrate, and sintering the mixture. However, the resistivity of the conventional moisture-responsive resistor element of this sinter type is very high, and the thickness and size should be increased so as to reduce the resistivity to a practically applicable level. Furthermore, in the conventional moisture-responsive resistor element, in order to increase the stability and prevent occurrence of polarization, an alternating current of a frequency of about 1 KHz is used for driving of the element. However, in case of alternating current driving, an oscillating circuit or the like should be disposed separately and the circuit structure is complicated. Furthermore, influences of oscillation on other proximity circuits should be taken into account and application of the conventional moisture-responsive resister element of the alternating current driving type involves various difficulties.